The present invention relates to the manufacture of wound thread packages in general, and more particularly to a method of and an apparatus for controlling the effective length of the thread wound into the respective package.
There are already known various arrangements for winding thread packages in yarn processing machines, among them such in which the package winding unit is so constructed that the package being formed is driven therein, preferably by frictional contact, by suitable driving means The present invention is intended primarily but not exclusively for use in a yarn processing machine that includes a plurality of yarn processing stations having independently operatable package winding units. Examples of such machines are rotor spinning machines, false twist texturizing machines, automatic back winding machines, air jet spinning machines, and friction spinning machines
It is a common practice in the thread winding field to use a friction drive roller (or "drum") for rotating a thread or yarn package during a winding operation with the drive roller being in a frictional contact with the package being formed or wound. In multi-station machines, in which a plurality of operating stations is arranged end-to-end in a row, a single common drive roller or shaft may be used to function as the aforementioned friction drive roller for all of the stations in the row, or each of the stations in the row may be provided with its own individual, independently drivable and stoppable, friction roller.
Even in those machine constructions in which the friction drive rollers of a plurality of operating stations are constituted by portions of a single rotatable shaft or roller, the wind-up sections of the operating stations will normally be independently operatable in the sense that a winding operation at one of the stations of the row may be commenced and terminated without affecting the winding operations taking place at the other stations associated with the same drive shaft or roller. This can be achieved quite simply by selectively terminating the supply of yarn at the individual stations and/or, preferably, by moving the yarn package out of contact with the friction drive shaft or roller at the station in the row at which the winding operation is to be terminated.
There is in existence an increasing trend in the field of manufacturing or upgrading the machines of this type for providing such machines with length control systems for determining the length of the thread being wound into each individual package. In the German published application DE-AS No. 22 16 960, and in the U.S. Pat. No. 3,988,879, there are disclosed length control systems wherein pulses emitted by a pulse emitter responsive to the rotation of a friction drive roller are accumulated in counter means. An adjustably settable correction factor can be set into the counter means so as to adapt the variable actual pulse count, which corresponds to the variable desired or required package length, to the capacity of the accumulator of the counting means, which capacity is limited or fixed. The aforementioned German application also suggests that the length of the thread wound per revolution of the drive roller or per pulse can be measured and used as input data in the calculation of the required setting for the adjustable counter.
It is also well known that friction drive systems suffer from the problem of slippage at the region of contact between the drive roller and the package being wound. Accordingly, the length of the thread wound per revolution of the drive roller depends not only on the diameter of the drive roller, but also on the degree of slippage between the drive roller and the package. This degree of slippage may vary during any individual winding operation, for instance, with an increasing pressure of the package being built up at the winding station. Furthermore, the degree of slippage may vary between successive winding operations if, for example, there is a change of the thread material between such successive operations, so that the friction conditions encountered at the contact region between the drive roller and the package being wound change accordingly.
A solution to this problem has been proposed in the published German patent application DE-OS No. 32 42 318. This system involves a continuous estimation of the degree of slippage during a winding operation. This estimation is then being used for modifying a signal which is representative of the rotation or the friction drive roller, so that the modified signal more accurately represents the wound length of the thread in the thread package. However, the system disclosed in this published application is quite complex and therefore too expensive to put into practicle operation. Furthermore, it can take into account only slippage, while other factors can also affect the "effective length" of a thread package during the uwinding of the latter, as will be further described later on in this specification.
While the system disclosed in the German patent application No. 22 16 960 could be so operated as to allow for the slippage and other factors which are present in the package drive system and influence the winding of the thread into the package, it is not specifically designed for that purpose and, therefore, it is not convenient to use by the machine operator or user, and is not particularly suited for use with equipment that handles data relating to the length of the thread being wound into the thread package.